Valeyard

The Valeyard is a fictional character from the long-running British science fiction television series, Doctor Who. He is described as an aspect of the Doctor from between his twelfth and final incarnations as depicted in the TV show or regenerations in the novelization of the story. In the serial The Trial of a Time Lord, comprising the whole of Season 23 of the series, the Time Lords appoint the Valeyard as prosecutor at the Sixth Doctor's trial, hoping to have him executed and thereby removing the sole witness to their near-destruction of life on Earth.